A variable valve timing control system in an engine is configured to change a rotational movement of a drive cam which is rotatable in association with a rotation of a crankshaft to a reciprocating movement of a valve by a pivot cam device. The variable valve timing control system is configured to change a pivot angle range of the pivot cam device to enable valve timing control according to an engine speed (see Japanese Laid-Open Patent Application Publication No. 2005-180232).
However, in such a variable valve timing control system, since a valve must be applied with a force from a spring to perform the reciprocating movement, a pressing force applied by a drive cam to another component positioned between the drive cam and the valve is large, and a sliding friction force generated on slide surfaces of the drive cam and another component, which are slidable relative to each other, is large. For this reason, the sliding surfaces tend to wear out and are low in durability.